Why do we get jealousy? I can feel it sometimes, too, but I don't know why. -Hailey, 10, London, Ontario

Cats love attention, but we don’t get jealous like humans do. It’s one of those emotions that set human beings apart from other creatures in the animal kingdom. But I can’t imagine it’s the most pleasant. The poet William Shakespeare once called jealousy a green-eyed monster. Still, it’s an emotion that can help you navigate the world. To learn more about it, I met up with my friend Craig Parks. He’s a psychology professor at Washington State University who studies how humans tick.

Humans have a whole history of emotions. Parks said one theory is that jealousy might be a “leftover” as humans evolved. Jealousy grows out of fear—especially fear that you might lose something that’s really important to you. Jealousy often brings with it other emotions including anger, fear, or loneliness, too.

“One of the reasons we get jealous is because we are always monitoring how we appear to others, how we measure and match up,” Parks said. He said if people weren’t constantly comparing, we’d probably see a lot less jealousy.

While humans don’t want to be an army of clones, they do want to fit into their world and make sense of it.

Parks said if your friend got an award and you didn’t, you might feel a little envious. But as the jealousy grew, you’d probably start to ask yourself some questions.

You’d wonder why you didn’t get the award and why she won instead. Your heart might start beating fast, your palms might get sweaty, and your pupils might get bigger. You might also fear that your family won’t be proud of you or that you’ll lose your friends.

These stories you make up are likely not true, explains Parks. But your brain starts making up stories to help you make sense of the situation.

There is still a lot of exploring to do when it comes to the brain. Scientists know the control center for emotions is the limbic system: in the middle of your three-pound, wrinkly brain there is a little almond-shaped part called the amygdala and next door is the hippocampus.

Every second, these parts are working together to help carry different kinds of messages to your body. These messages bring information about how you’re doing and help you decide what move to make next.

“And one of the things we don’t like to say is that we don’t know,” Parks said.

Parks said it can be uncomfortable to not know what’s coming in the future. Fear is a place where the green-eyed monster of jealousy likes to hang out. It’s an emotion that pretty much every human being feels, though. So I’m glad you can recognize it and that you are brave enough to ask tough questions.